Printer

ABSTRACT

A printer for application of droplets of hot melt ink on a substrate in order to generate characters or symbols thereon includes a compact and space saving housing containing a reservoir for supply of the hot melt ink in a solid state, a feeder for reception of the hot melt ink in the solid state form the reservoir, and a printhead having one or several discharge nozzles. Between the feeder and the printhead a chamber is provided in the housing and the feeder is adapted to feed the hot melt ink by means of positive displacement to the chamber while the ink is melted by a heater arranged in the housing. The printhead receives the hot melt ink in a melted state from the chamber and discharges it in the form of droplets from the nozzles for application on the substrate. The reservoir includes perforations to allow carrier gases to escape.

The subject invention concerns a printer designed to apply droplets ofhot melt ink onto a substrate in order to generate characters or symbolsthereon.

In one prior-art device incorporating a printer for the purposesmentioned, an external reservoir is immersed in a hot water bath or thelike and is connected via a comparatively long hose or tube to theprinter proper, the latter having a print-head including one or severaldischarge nozzles.

Hot melt ink in solid form is supplied to the reservoir in which the hotmelt ink melts when affected by the hot water bath and from whence themolten hot melt ink is transferred via the hose or the pipe to theprinter itself to be applied on the substrate.

In order to prevent the molten hot melt ink from returning to the solidphase while being advanced inside the hose or the pipe or inside theprinter, the hose or pipe as well as the printer must be kept heated,which may be effected by means of infra-red radiation or other heatingarrangements.

A serious drawback found in this prior-art device is that it is composedof several spaced apart, separate components which in addition must bemaintained in a heated condition along the entire and comparatively longpath of travel of the molten hot melt ink from the reservoir to theprint-head. The heating causes problem also because the heat energyinput must be comparatively high in view of the heat losses to theenvironment.

The purpose of the subject invention is to avoid the disadvantages andthe problems inherent in the prior-art device and to provide a printerwhich is complete in itself while at the same time it is compact andefficient.

The purpose is achieved in a manner which is as simple as it isingenious in that the printer has a housing in which are provided areservoir having an inlet for supply of the hot melt ink in solid stateand an outlet, a feeder adjacent the reservoir outlet, said feederhaving an inlet for reception of the hot melt ink in solid state fromthe receiver and an outlet, a heater, and a print-head having an inletwhich is connected to the feeder outlet and at least one dischargenozzle, said feeder supplying the hot melt ink, preferably by positivedisplacement, to the print-head while the ink is being melted with theaid of the heater, said print-head receiving said molten hot melt inkfrom the feeder and discharging it in the shape of droplets from thedischarge nozzle for application of said droplets on the substrate.

The invention will be described in closer detail in the following withreference to the accompanying drawing, which in a longitudinal sectionalview schematically. illustrates a presently particularly preferredembodiment of the printer, the rear end of which, appearing to theright-hand side of the drawing, being cut away.

The printer designed generally on the drawing figure by referencenumeral 1, is designed for application of molten hot melt ink 2 in theform of droplets 3 onto a substrate 4, such as e.g. paper, cardboard orthe like which may be used to form packages of various kinds, primarilyfor foodstuff, in order to generate symbols or characters on saidsubstrate 4. When the droplets 3 hit the substrate 4 they solidify asthey are cooled on impact.

When the substrate 4 has an external protective plastic film, whichoften is the case in connection with foodstuff packages, the dropletsare etched to the film as the latter softens or melts when hit by thedroplets. The characters or symbols thus produced become forgery-proofin that if one tries to remove them from the substrate, they leavebehind an identifiable impression in the subjacent plastic film or evenon the packaging material itself.

In accordance with the embodiment illustrated, the printer 1 comprises ahousing 5 of an essentially circular cylindrical shape, and a cover 7positioned at a distance 6 from and around the housing.

The housing 5 has a tubular jacket 8 of a suitable material, such asaluminium, and at its rear (right-hand side in the drawing figure) thetubular jacket 8 is connected to an end wall, not shown, and at itsfront to a disc-shaped partition wall 9, for instance of aluminium orother suitable material.

Between the end wall and the partition wall 9 a likewise disc-shapedpartition wall 10, also of aluminium, is provided. This wall, too, thusis positioned within the tubular jacket 8.

In the space 11 between the partition wall 9 and the partition wall 10 areservoir 12 is located, said reservoir having an inlet 13 for supply ofthe hot melt ink 2 in solid state 14 from a storage, not shown, via atube 15 or the like. The inlet 13 is provided in the partition wall 10,said wall also forming one, 16, of the two end walls 16 and 17 of thereservoir 12. In the opposite end wall 17 of the reservoir 12 an outlet18 to be described in the following, is provided.

In accordance with the illustrated embodiment, the hot melt ink 2 insolid state 14 is intended to be supplied to the reservoir 12 from thestorage in the shape of granules together with a carrier gas 19, such aspressurized air. For this purpose, the reservoir 12 is equipped with ajacket 20 in which perforations 21 are formed to allow discharge fromthe reservoir of the carrier gas 19 supplied thereto. Preferably, theperforations are in the shape of a gas-pervious net which thus forms thejacket 20 of the reservoir 12.

The granular material used presently has an average diameter ofapproximately 0.3-0.5 mm. and the gas-pervious net 20 consequently has amesh size smaller than the average diameter of the granules.

The carrier gas 19 emitted from the reservoir may flow out of thehousing 5 to the environment via apertures 22 formed in the tubularjacket 8.

Instead of having a positive pressure as suggested above, the carriergas 19 could have a negative pressure, that is, be sucked into thereservoir 12 together with the granules. In this case a suction means,not shown, may be provided in the space 11, for instance an ejectorwhich creates a negative pressure inside the reservoir 12.

Another possibilitiy is to configure the reservoir 12 as a completelyclosed and pressure-tight container which is subjected to a positivepressure and may be equipped with a sluice valve or an equivalent means,allowing the granular material to be supplied in batches or continously.In this manner the positive pressure forces the granules to advance inthe direction towards the outlet 18 of the reservoir 12.

Another possible solution is to supply the hot melt ink 2 in solid state14 to the reservoir 12 in the shape of rods or the like instead of inthe shape of granules.

Inside the housing 5, in the area of the outlet 18 of the reservoir 12,a feeder, generally designated by numeral 23, is located, said feederhaving an inlet 24 for reception of the hot melt ink 2 in solid state 14from the reservoir, and an outlet 25.

More precisely, the feeder in accordance with the illustrated embodimentis configured as a screw worm 26 which is rotationally mounted in anenclosing housing 27.

Via a drive shaft 26 extending through the partition wall 10, the screwworm 26 is rotated by an electric motor 29, the latter being positionedin the space 30 between the partition wall 10 and the rear end wall, notshown, of the housing 5, and being electrically connected to a source ofelectricity, not shown, by means of electric wires 31.

The housing 27 of the feeder 23 is formed with one or several apertures32 positioned inside the reservoir and forming the feeder inlet 24 forreception of the hot melt ink 2 in solid state 14 from the reservoir 12and for transport of the ink by means of the screw worm 26 along thehousing 27 in the direction towards the feeder outlet 25.

It is quite possible to design the feeder 23 differently from theconfiguration described in the afore-going. For instance, instead of thescrew worm 26 and its housing 27 a piston, arranged for reciprocatingmovement inside a cylinder, could be used. Alternatively, the feedercould be designed as one or several elongate channels through which thehot melt ink 2 is conveyed under the influence of the positive pressureinside the reservoir 12 when the latter is configured in accordance withthe pressurized embodiment described previously.

Downstream of the reservoir 12, inside the housing 5, there is provideda heater, generally designated by 33. In accordance with the embodimentillustrated the heater is formed by a comparatively thick disc-shapedheating block 34 of a material possessing good heat conductingproperties.

In order to insulate the reservoir 12 as well as the other components inthe housing upstream of the heater 33 from the heat generated by thelatter, heat insulation 35 in the form of a disc-shaped plate 36 isprovided. The plate may be made from a heat-insulating plastic, such asbakelite, and it is mounted inside the housing 5 intermediate thereservoir 12 and the heater 33.

An electric heating cartridge 37 is positioned in a recess in theheating block 34 in order to heat the latter, said heating cartridgebeing electrically connected to the power source, not shown, by means ofelectric wires 38.

As appears from the drawing, the heating block 34 encloses and heats thefeeder 23 downstream of the heat insulation 35, with the result that thehot melt ink 2 changes from its solid state 14 to a liquid or moltenstate 39 before reaching the outlet 25 of the feeder 23.

The temperature of the hot melt ink 2 in liquid state 39 varies as afunction of the composition of the hot melt ink but generally speakingthe melting temperature ranges from a minimum of about 70° C. to amaximum of about 180° C. for hot melt inks available at present. Inpractice, the temperatures used range from about 120° to about 150° C.

The housing 5 also includes a print-head, generally designated byreference 40, which forms the front end (left-hand end on the drawingfigure) of the printer 1. The print-head 40 has a rear inlet 41 whichvia a channel 42 is connected to the outlet 25 of the feeder 23, and atleast one front discharge nozzle 43 from which droplets 3 of the moltenhot melt ink 2 are discharged to be applied on the substrate 4.

Since the print-head 40 does not form part of the subject invention andis of a more or less conventional construction it will not be describedin any detail herein.

Inside the channel 42, intermediate the outlet 25 of the feeder 23 andthe inlet of the print-head 40 a chamber, generally designated byreference 44, is provided in accordance with the embodiment illustrated.The chamber is divided into one pressure part 45 and one actuating part46. These parts 45, 46 are separated by a diaphragm 47 of an resilientand impervious material, such a rubber of a quality that withstands thehigh temperature of the melted hot melt ink 2.

The pressure part 45 has an inlet 48 and an outlet 49 and the inlet 48is connected to the part of the channel 42 that extends between thepressure part and the outlet 25 of the feeder 23, whereas the outlet 49is connected to the channel part extending between the pressure part andthe inlet 41 of the print-head 40.

The actuating part 46 of the chamber 44 encloses an actuating means 50in the shape of a compression spring which is held between the diaphragm47 and the opposite side or bottom 51 of the actuating part 45 to act onthe diaphragm with an adjustable force and accordingly to effectvariable pressurization of the melted hot melt ink 2 in the pressurepart 45.

An operating element 52 in the form of a rod extending through theheater 33, the heat insulation 35, and the partition walls 9 and 10connects the compression spring 50 to a regulating means 53 which ishoused in the space 30. The regulating means 53 consists of a switch 54which via electric wires 55 is electrically connected to the electricmotor 29 for operation of the screw worm 26 inside the feeder 23.

When the electric motor 29 is energized and rotates the screw worm 26,the volume of the pressure part 45 of the chamber 44 increases as thehot melt ink 2 in melted state 39 is supplied thereto. The diaphragm 47consequently will bulge increasingly into the actuating part 46 againstthe action of the spring 50. At the same time the diaphragm will pushthe rod 52 to the right as seen in the drawing figure, to a positionwherein the switch is affected and interrupts the supply of electricityto the electric motor 29 with consequential stop of the screw worm 26.

When the print-head 40 in the conventional manner receives a signal todischarge droplets 3 of melted hot melt ink 2 from the discharge nozzle43 in order to generate symbols or charactaers on the substrate 4 thevolume of the pressure part 45 of the chamber 44 gradually is reduced asthe hot melt ink 2 in melted state 39 is being consumed. Under theinfluence of the spring 50 the diaphragm therefore will bulgeincreasingly into the pressure part 45, bringing along the rod 52 in itsmovement, to the left as seen in the drawing figure, to anotherposition, wherein the switch is again actuated and re-establishes theelectricity supply to the electric motor 29, whereby the screw worm 26again starts feeding the pressure part with melted hot melt ink.

This procedure is repeated and in response to the requirement of theprint-head to be supplied with hot melt ink 2 in melted state 39 fromthe pressure part 45 the screw worm 26 may operate from an almostcontinuous mode to one involving rather brief operational steps.

In cases when the feeder 23, as mentioned previously, is configuredotherwise than as a screw worm 26, for example in accordance with theembodiment comprising channels and a pressurized recevoir 12, thechamber 44 as well as the actuating and operational componentsassociated therewith for controlling the operation of the electric motor29, may be superfluous and therefore could be eliminated.

I claim:
 1. A printer designed to apply droplets of hot melt ink onto asubstrate in order to generate characters or symbols thereon,characterized by a housing, in which are provided a reservoir having aninlet for supply of the hot melt ink in solid state and an outlet, thehot melt ink in solid state is arranged to be supplied to the reservoirin the form of granules together with a carrier gas, and in that saidreservoir is provided with perforations to allow escape of said carriergas supplied thereto, a feeder adjacent the reservoir outlet, saidfeeder having an inlet for reception of the hot melt ink in solid statefrom the receiver and an outlet, a heater, and a print-head formed withan inlet which is connected to the feeder outlet and with at least onedischarge nozzle, said feeder supplying the hot melt ink to theprint-head while the ink is being melted with the aid of the heater,said print-head receiving said molten hot melt ink from the feeder anddischarging said hot melt ink in the form of droplets from the dischargenozzle for application of said droplets on the substrate.
 2. The printeras claimed in claim 1, wherein the feeder is configured as a worm screwwhich is driven by a motor and which is rotatably mounted inside ahousing, said housing being formed with at least one aperture positionedin the reservoir and forming the feeder inlet opening to allow said wormscrew to receive hot melt ink in solid state form from the reservoir andto transport said ink along the reservoir in the direction towards thefeeder outlet.
 3. The printer as claimed in claim 1, wherein the heateris a heating block enclosing and heating the feeder downstream of theheat insulating means and melting the hot melt ink therein before theink reaches the feeder outlet.
 4. A printer as claimed in claim 1,characterized in that the perforations in the reservoir (12) are formedby a net (21) forming the jacket (20) of the reservoir, and in that thegranules have an average diameter size ranging from about 0.3 to 0.5 mm,the mesh size of said net being smaller than said average diameter.
 5. Aprinter as claimed in claim 4, characterized in that the feeder (23) isconfigured as a screw worm (26) which is driven by a motor (29) andwhich is rotatably mounted inside a housing (27), said housing beingformed with at least one aperture (32), said aperture positioned in thereservoir (12) and forming the feeder inlet opening (24) to allow saidscrew worm to receive hot melt ink (2) in solid state (14) from thereservoir and to transport said ink along the reservoir in the directiontowards the feeder outlet (25).
 6. A printer as claimed in claim 5,characterized in that the heater (33) is a heating block (34) enclosingand heating the feeder (23) downstream of the heat insulating means (35)and melting the hot melt ink (2) therein before the ink reaches thefeeder outlet (25).
 7. A printer as claimed in claim 6, characterized inthat an electric heating cartridge (37) is arranged inside the heatingblock (34) to heat the latter.
 8. A printer as claimed in claim 7,characterized in that the housing (5) also encloses a chamber (44)positioned intermediate the feeder (23) and the print-head (40) andhaving an inlet (48) which communicates with the feeder outlet (25) andan outlet (49) which communicates with the print-head inlet (41).
 9. Aprinter as claimed in claim 8, characterized in that the chamber (44) isdivided into one pressure part (45) and one acutating part (46), saidparts being separated from one another by a diaphragm (47), and in thatthe inlet and the outlet (48 and 49, respectively) of the chamberrespectively debouches into and departs from the pressure part, and inthat the actuating part houses an actuating means (50) adapted toadjustably actuate the diaphragm and consequently to effect variablepressurization of the hot melt ink (2) inside the pressure part.
 10. Aprinter as claimed in claim 9, characterized in that the actuating means(50) is arranged in yieldable abutment against the diaphragm (47) and isconnected to a regulator means (53) via an operating means (52), saidregulating means (53) being positioned inside the housing (5) upstreamof the heat insulating means (35) and being connected to the motor (29)driving the screw worm (26), in order to start and stop the motor inresponse to the pressure inside the pressure part (45).
 11. A printer asclaimed in claim 4, characterized in that the heater (33) is a heatingblock (34) enclosing and heating the feeder (23) downstream of the heatinsulating means (35) and melting the hot melt ink (2) therein beforethe ink reaches the feeder outlet (25).
 12. A printer as claimed inclaim 5, characterized in that the heater (33) is a heating block (34)enclosing and heating the feeder (23) downstream of the heat insulatingmeans (35) and melting the hot melt ink (2) therein before the inkreaches the feeder outlet (25).
 13. The printer as claimed in claim 1,wherein the housing also encloses a chamber positioned intermediate thefeeder and the print-head and having an inlet which communicates withthe feeder outlet and an outlet which communicates with the print-headinlet.
 14. A printer designed to apply droplets of hot melt ink onto asubstrate in order to generate characters or symbols thereon,characterized by a housing, in which are provided a reservoir having aninlet for supply of the hot melt ink in solid state and an outlet, thehot melt ink in solid state is arranged to be supplied to the reservoirin the form of granules together with a carrier gas, and in that saidreservoir is provided with perforations to allow escape of said carriergas supplied thereto, a feeder adjacent the reservoir outlet, saidfeeder having an inlet for reception of the hot melt ink in solid statefrom the receiver and an outlet, a heater, and a print-head formed withan inlet which is connected to the feeder outlet and with at least onedischarge nozzle, and a heat-insulating means arranged inside thehousing, between the reservoir and the heater, in order to insulate thereservoir from the heat from the heater, said feeder supplying the hotmelt ink to the print-head while the ink is being melted with the aid ofthe heater, said print-head receiving said molten hot melt ink from thefeeder and discharging said hot melt ink in the form of droplets fromthe discharge nozzle for application of said droplets on the substrate.15. A printer as claimed in claim 14, characterized in the feeder (23)is configured as a screw worm (26) which is driven by a motor (29) andwhich is rotatably mounted inside a housing (27), said housing beingformed with at least one aperture (32), said aperture positioned in thereservoir (12) and forming the feeder inlet opening (24) to allow saidscrew worm to receive hot melt ink (2) in solid state (14) from thereservoir and to transport said ink along the reservoir in the directiontowards the feeder outlet (25).
 16. A printer as claimed in claim 14,characterized in that the heater (33) is a heating block (34) enclosingand heating the feeder (23) downstream of the heat insulating means (35)and melting the hot melt ink (2) therein before the ink reaches thefeeder outlet (25).
 17. A printer as claimed in claim 14, characterizedin that the housing (5) also encloses a chamber (44) positionedintermediate the feeder (23) and the print-head (40) and having an inlet(48) which communicates with the feeder outlet (25) and an outlet (49)which communicates with the print-head inlet (41).